EVIDENCE FOR MULTIPLE BINDING-SITES FOR SEVERAL COMPONENTS OF HUMAN LYMPHOBLASTOID INTERFERON-ALPHA

The antiproliferative and competitive binding activities of 20 purifie d components of human lymphoblastoid interferon (IFN)-alpha were compa red with that of recombinant human IFN-alpha2b on Daudi and AU937 cell s. We observed broad ranges of antiproliferative activities of the IFN -alpha components on these cell lines. Daudi cells were more sensitive to the IFN-alpha components than AU937 cells; the concentrations of t he components that resulted in 50% inhibition of cell growth ranged fr om 0.003 ng/ml to >10 ng/ml on Daudi cells and 0.05 ng/ml to >200 ng/m l on AU937 cells. Component o was the most active human IFN-alpha on b oth cell lines. Scatchard analysis demonstrated that the number of IFN -alpha2b binding sites is greater on Daudi cells (12,700 binding sites /cell) than AU937 cells (3,300 binding sites/cell); however, their rec eptor affinities were similar. Component o, which exhibited high antip roliferative activity on both cell lines, had low affinity for the IFN -alpha2b binding site on AU937 and Daudi cells. Several human IFN-alph as (components b', b'', and e) appeared to have high affinity binding sites but low antiproliferative activity on both Daudi and AU937 cells . These data suggest that there may be more than one binding site or r eceptor for human IFN-alpha, and/or there may be a multicomponent rece ptor involved in the biological actions of these molecules.